What are referred to as cross belt sorters are known from piece goods conveyor technology, in particular sorting technology, and are composed of vehicles which can be moved on a conveyor system, usually a plurality of which vehicles are joined to form a train or a chain of carriages which circulates continuously. The individual vehicles are provided with carrier belts, which can be driven so that they circulate transversely with respect to the direction of transportation of the vehicles. On this carrier belt, also referred to as a cross belt, the piece goods are conveyed in the longitudinal direction of the conveyor with the cross belt in the stationary state, and for the purpose of sorting at the desired unloading location the piece goods are discharged laterally through controlled driving of the cross belt transversely with respect to the direction of transportation of the cross belt conveyor.
In order to activate the described discharging process, a drive for the cross belt, which can be activated at least at the unloading and/or loading location, has to be provided on each carriage of the moving chain of carriages of the cross belt sorter.
Various drives are known for this purpose. It is very widespread practice to implement the drive with electric motors which are carried along on each carriage and which tap their power via contact collector lines laid along the conveyor track or inductively (EP 0 990 604 A1).
It is also known to use the propulsion of the chain of carriages itself to activate the discharging of goods. In this context, for example a shiftable connector link is connected by means of a press fit to a friction wheel by means of which the discharging process is initiated at the unloading location as the chain of carriages passes by (DE 198 01 706 A1).
An electric motor for activating the drive for the cross belt must be capable of discharging piece goods up to a weight of 50 kg with an acceleration of up to 3 m/s2. The power required for this has to be transmitted to the moving chain of carriages via contact collector lines or in a contactless fashion; in addition, the information as to when the respective cross belt is to be moved must also be transmitted to the moving chain of carriages. A considerable degree of expenditure is therefore necessary and this makes the device significantly more expensive and susceptible to faults.
If the cross belt is activated mechanically, it has been found that the operative principle functions reliably only up to a speed of 1.6 m/s because the jolting acceleration of the cross belt which is induced by the friction wheel has an adverse effect on the discharging behavior, in particular in the case of lightweight consignments. For this reason, sorting speeds up to 2.5 m/s have previously been implemented with an electric drive.